Abstract Coastal geomorphic systems have been studied widely to understand the responses of shorelines to fluctuating sea levels. Submerged shorelines, remnant of Pleistocene sea-level lowstands, are well preserved on the South African continental shelf. This paper describes work undertaken to better understand offshore coastal environments now submerged by high sea levels off the South African south coast near Mossel Bay, offshore of the Pinnacle Point archaeological locality. Multibeam bathymetry and side-scan sonar reveal evidence of past sea-level fluctuations and submerged coastal landscape features on the seabed. These results form the basis of an ongoing palaeoenvironmental reconstruction for this part of the shelf. We describe seven significant geomorphic features that show a submerged environment that differs significantly to the immediate adjacent coastal plain. However, these features are comparable to other stretches of the present South African shoreline that serve as modern analogues. We propose that features on the continental shelf primarily reflect geological substrate, gradients and Pleistocene sea-level fluctuations. Early modern humans were likely to have had a different set of resources to use in this Pleistocene landscape compared to those available along the presently exposed coast.

Abstract A 1.2-km-thick section of the Miocene Monterey and overlying Pliocene Sisquoc formations in the Santa Maria basin area of California contains highly variable amounts of biogenic silica, detrital clay and silt, organic matter, carbonate, pyrite, and francolite. Organic-matter diagenesis resulted in the early precipitation of dolomite, pyrite, and francolite, and the concentration of trace metals. Dolostone horizons occur 1 to 10 m apart and consist of 50 to 95 weight percent pore-filling dolomite. The dolomite is low in Fe and Mn and contains an average of 0.8 to 5.3 mole percent excess Ca. Dolomite composition is related to texture in some samples and suggests several different episodes of dolomitization. There is a positive correlation between organic matter, pyrite, and the trace metals V, Cr, Ni, Cu, and Zn. Pyrite formation probably occurred below the sediment/seawater interface (noneuxinic basin) in the microbial-sulfate reduction zone, and was limited by Fe in sediment having a high organic matter-to-clay ratio and by reduced sulfur in sediment having a low organic matter-to-clay ratio.